This invention relates to a method and apparatus for observing bore holes such as boring holes and pipe holes.
In drilling underground cavities for dams, tunnels and the like, a geological survey is performed at the site and the results of the survey are reflected in the design drawings. It is also necessary to select the method of executing the project and to assure perfection in terms of how the project proceeds, project safety measures and the like.
In a geological survey, it is generally necessary to ascertain the direction, inclination of rock joint and properties of the rock, as well as strike and dip of the bed. One method of performing such a survey is to bore a hole at the site and sample the core in order to observe its nature. Another method is to bore a hole at the site and make a direct observation of the bore hole wall.
Bed formations exhibit a variety of different colors depending upon the type of rock and the degree to which the rock has weathered. For example, granite in fresh rock is white or blue-white in color but changes to yellow and then to brown as weathering progresses.
In the first method of geological surveying that relies upon the direct observation method, an engineer will pass judgment on the type and category of rock by observing, with the naked eye, rock and exposed rock surfaces to check for the color variations mentioned above, and by examining rock hardness using a hammer tapping method. The results of these tests are recorded. In a boring survey, the results are usually recorded in a boring logging.
An example of a boring log is illustrated in FIG. 1. As shown, the results recorded include the name of the bed formation, color tone, core sampling rate and RQD, as well as the results of electrical logging, temperature logging and sonic logging. The core sampling rate and RQD are indicated in terms of curves expressing the percentage (%) of the core per one length of penetration, and the electrical, temperature and sonic surveys are indicated by the curves or broken lines expressing .rho.(.OMEGA.-m), T(.degree.C.) and V(Km/sec), respectively. For the names of the bed formations and soil nature, detailed category tables are used regarding soil category and rock.
As for color tone, however, measures regarding methods of expression and measurement have not yet been firmly established, and color tones that can serve as criteria for judgment of color following weathering cannot be discriminated objectively when observation is performed by the naked eye. Consequently, color tone is judged and recorded based on the subjectivity of the engineer. Accordingly, even if a bed of one and the same color is observed and the color recorded in a table, it is rare for the same expression to be used by different engineers because of the difference among individuals. This results in the use of subjective expressions and the use of a variety of different color names. Moreover, it is impossible to reproduce a color based merely on a written entry.
Even if data from examination of soil quality and underground water are obtained by performing electrical logging and sonic logging in the boring hole and sampling objective data continuously in the direction of bore depth, therefore, it is not possible to put these data into the form of continuous numerical values with regard to color tone.
In conducting boring investigations, moreover, the boring core must be extracted and brought above ground in order to be observed. In doing so, a core that has undergone severe weathering tends to crumble so that portions thereof cannot be observed, and data indicative of the core constitution cannot be sampled in a continuous manner; instead, the data obtained is the mean of values obtained from individual layers.
In the second method of geological surveying that entails direct observation of the bore hole wall, observation of the bore hole wall.
A bore hole television is a compact color television camera suspended from cables and lowered into the bore hole so that the bore hole wall can be viewed on a television monitor above ground. Since a bore hole television has an angle of view of about 30.degree., the entire periphery of the bore hole wall is observed by rotating a mirror mounted on the front end of the camera. When performing an analysis of the wall, the wall is photographed one frame at a time by the television camera and the frames are assembled into an expanded picture, as illustrated in FIG. 2. In order to obtain a record of these pictures, they are recorded using an VTR. Compass direction is indicated in the picture in the form of an angle of rotation from due north.
A bore hole periscope is a periscope inserted into the bore hole and includes a head comprising an objective lens and a reflector. A pipe is connected to the head and permits one to observe the bore hole wall above ground by looking into an eyepiece lens. Like the bore hole camera, the bore hole periscope has an angle of view of about 30.degree.. In order to observe the entire periphery of the wall, the observer must rotate the entire periscope from above ground. Recording pictures using such a periscope entails mounting a camera on the eyepiece portion thereof and photographing the necessary areas of the wall. Compass direction is ascertained by attaching a magnet to the eyepiece portion of the periscope and reading the position of a needle by the naked eye.
A bore hole camera includes a head accommodating a panoramic camera. The head is suspended from cables and lowered into the bore hole to take expanded pictures of certain sections of the bore hole wall. These pictures are recovered and reproduced on film to obtain an expanded picture. The width of an expanded picture taken by one revolution of the bore hole camera is 1 to 1.5 cm, so that about a 50 cm section of the wall can be photographed on a single roll of film. To acquire a succession of expanded pictures, therefore, the pictures having the width of 1 to 1.5 cm must be assembled vertically. Compass direction is indicated by reproducing the direction of due north on the film.
A bore hole scanner includes an optical head and a photoelectric transducer. While being rotated, the optical head projects a light beam onto the bore hole wall. Light reflected from the wall is received by the photoelectric transducer, which proceeds to convert the reflected light into an electric signal. An expanded picture is obtained from the direction of the projected light beam and the depth of the scanner.
In order to ascertain the direction and dip of cracks and of the bed formation, it is preferred in terms of accuracy and efficiency that an expanded picture be produced and that this be observed in its entirety. With the conventional bore hole television and bore hole periscope, however, all of the pictures taken cannot be observed in a single viewing. Accordingly, the pictures must be assembled by being pasted together, as shown in FIG. 2, in order to obtain the expanded picture. This requires a considerable amount of labor. The bore hole camera, on the other hand, allows a picture of the entire bore hole periphery to be obtained in a comparatively simple manner. However, only about a 50 cm section can be measured at a time and the head must be lifted out of the bore hole and then reinserted whenever the film is replaced. In addition, since the quality of the expanded picture cannot be verified without first developing the film, judgment of picture quality cannot be made at the site. If a usable picture fails to be obtained, it is necessary to return to the site and repeat photography.
Among the items of equipment mentioned so far, the bore hole scanner is best in that an expanded picture can be acquired at the time the measurement is taken. Still, a disadvantage with this expedient is that a hard copy of the overall expanded picture cannot be obtained with a display device of this kind.
When conducting a geological survey by lowering number of revolutions of a pulley used for depth measurement. Measurement of depth by relying upon such a pulley is prone to error owing, for example, to pulley slippage.
To correct for errors ascribable to factors such as pulley slippage, one method adopted is to affix markers to the lowering cable at fixed intervals along its length. In surveys of structures related to civil engineering, depths reach down to some 300 meters. With the abovementioned marker method, depth can be determined to within a measured precision of .+-.1 meter. This will provide values which, by and large, are accurate enough for use in constructing structures of the above type. Recently, however, the need has arisen for investigative borings in civil engineering works involving depths of 1000 to 1500 meters. For depths of the 1000-meter class, the aforementioned conventional approaches involve considerable difficultly in terms of accuracy. Specifically, since the cables used stretch due to their own weight, it becomes impossible to ascertain depth in a precise manner where the deeper bore holes are concerned.
At larger boring lengths, there are occasions where the hole is drilled while developing an irregular curve. This can be caused by crushed rock fragements becoming lodged in the vicinity of the drill bit, by differences in drilling resistance when drilling obliquely through bed interfaces having different hardnesses, or by deviations in the deformation characteristic of the boring rod material. This leads to a problem wherein the geological information obtained by boring represents neither the correct coordinates nor the correct direction. In order to reduce the cost of boring oil and geothermal wells, moreover, the boring tip is pointed in a number of different directions by curving the hole artificially in mid-course from a single entrance. In this case also it is necessary that hole curvature be accurately measured.
One example of measuring bore hole curvature is to lock a gyrobalancer, to which a magnetic rotary body is attached, at an observation position. Other systems for measuring bore hole curvature include a so-called "toropari" for taking pictures, a dipmeter in which a weighed needle is lowered onto a recording paper, which is rotated by a magnetic system, in order to perforate or mark the paper so that dip can be ascertained, or a gyro that traces hole curvature by a tridirectional gyro. All of these conventional systems have problems, however. For example, with the system using the "toropari" or dipmeter, data can be acquired neither continuously nor instantaneously. The gyro system is not only costly but also places a limitation upon speed at measurement in order to improve precision. The gyro must also be calibrated with each use.